Problem: If $a + b = 4$ and $x + y = -2$, what is $-5x + 10b + 10a - 5y$ ?
Explanation: $= 10a + 10b - 5x - 5y$ $= (10) \cdot (a + b) + (-5) \cdot (x + y)$ $= (10) \cdot (4) + (-5) \cdot (-2)$ $= 40 + 10$ $= 50$